Acoustic wave storage convolver

Abstract

An acoustic wave storage convolver includes a plurality of sampling transducers coupled to a surface wave propagating medium along a path defined by a pair of opposedly disposed input transducers. The sampling transducers, each of which is connected to a suitable signal storage element, are equally spaced along the path by an integral number of acoustic wavelengths plus or minus 1/4 wavelength for providing successive samples of surface waves propagated along the medium in phase quadrature relationship. Means initiating the signal storage function and output means developing the convoluted product of two high frequency signals applied to the input transducers are provided.

What is claimed is: 
     
       1. In an acoustic wave storage system of the type having means comprising a plurality of signal sampling elements disposed in association with the surface of an acoustic wave propagating medium for sampling surface waves propagated along said surface having an acoustic wavelength d 0  and having means for storing the values of said sampled surface waves for subsequent processing, the improvements wherein said elements are spaced for sampling said surface waves at successive points along said surface separated by substantially (n/2 + 1/4) d 0 , where n is an integer. 
     
     
       2. The improvement according to claim 1 including input transducer means coupled to said surface and responsive to input signals applied thereto for launching said surface waves, said input signals comprising an rf carrier modulated by a baseband signal having a nominal bandwidth, said element spacing defining a spatial sampling frequency f s  selected such that f s  is greater than or equal to about four times said nominal bandwidth and said acoustic wavelength d 0  being selected such that d 0  = v 0  /f s  (n/2 + 1/4), where n is an integer and v 0  is the characteristic propagation velocity of said medium. 
     
     
       3. The improvement according to claim 2 wherein said signal sampling elements comprise a plurality of interdigitated comb-type electro-acoustic transducers coupled to said medium, each of said transducers having a series of uniformly interdigitated fingers extending transversely of the direction of wave propagation along said surface. 
     
     
       4. The improvement according to claim 2 wherein said sampling frequency f s  and the frequency of said rf carrier comprise respectively 20MHz and 45MHz and wherein each of said transducers comprises a five finger structure having an optimum response to acoustic waves propagated along said medium at a frequency of 50MHz. 
     
     
       5. An acoustic wave storage convolver comprising: a surface-wave propagating medium;   first and second input transducers coupled to one surface of said medium for launching surface waves in opposite directions along a path therebetween in response to the application of, respectively, first and second path signals, said surface waves having an acoustic wavelength of d 0  ;   a plurality of cells each comprising a transducer and storage means responsive thereto, said transducers being coupled to said one surface along said path and spaced by at least 3/4 of said acoustic wavelength d 0  for providing successsive samples of said surface waves in phase quadrature relationship;   means coupled to said cells operable for simultaneously causing said storage means to store the outputs of said transducers in response to surface waves launched by one of said input transducers; and   output means for convolutely combining said stored outputs with the outputs developed by said transducers in response to surface waves launched by the other of said input transducers.   
     
     
       6. The acoustic wave storage convolver according to claim 5 including an electrode disposed adjacent the other surface of said medium and forming with said transducers a plurality of capacitors C p  each coupled to a respective one of said storage means. 
     
     
       7. The acoustic wave storage convolver according to claim 6 wherein each of said storage means comprises a storage diode having a reverse bias capacitance of C 1  and wherein the interelectrode capacitance of adjacent ones of said transducers is represented by C s , components being selected such that C p  = C 1  = C s  /3. 
     
     
       8. The acoustic wave storage convolver according to claim 5 wherein said first and second input signals each comprise an rf carrier modulated by a baseband signal having a nominal bandwidth and wherein said transducer spacing defines a spatial sampling frequency f s , said sampling frequency being selected such that f s  is greater than or equal to about four times said nominal bandwidth. 
     
     
       9. The acoustic wave storage convolver according to claim 8 wherein said transducers comprise a plurality of comb-type interdigitated electro-acoustic transducers coupled to said medium, each of said transducers having a series of uniformly interdigitated fingers extending transversely of the direction of wave propagation along said surface. 
     
     
       10. The acoustic wave storage convolver according to claim 9 wherein said sampling frequency f s  and the frequency of said rf carrier comprise respectively 20MHz and 45MHz and wherein each of said transducers comprises a five finger structure having the optimum response to acoustic waves propagated along said medium at a frequency of 50MHz.